Several efforts have been made to use technology to encourage people to buy more environmentally sustainable food. However, only a small amount of research has attempted to understand the roles of technology in food shopping by incorporating perspectives from various stakeholders. We aimed to explore how the design space for future technology in sustainable food shopping is negotiated among sustainability-aware individuals, sustainability professionals, and designers through co-design workshops and speculative enactments. We identify three roles of technology in sustainable food shopping: technology as guidance, technology as mediator, and technology for reflection. Additional insights are provided regarding how parts of these roles for future technology are rejected, adopted, or adjusted when enacted in everyday food shopping. We discuss design implications for the roles of sustainability technology in terms of data accuracy and transparency, as well as embodied data experiences. Furthermore, we provide methodological considerations for speculative enactments in SHCI.